A communication device can be understood as a device provided with appropriate communication and control capabilities for enabling use thereof for communication with others parties. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on. A communication device typically enables a user of the device to receive and transmit communication via a communication system and can thus be used for accessing various service applications.
A communication system is a facility which facilitates the communication between two or more entities such as the communication devices, network entities and other nodes. A communication system may be provided by one more interconnect networks. One or more gateway nodes may be provided for interconnecting various networks of the system. For example, a gateway node is typically provided between an access network and other communication networks, for example a core network and/or a data network.
An appropriate access system allows the communication device to access to the wider communication system. An access to the wider communications system may be provided by means of a fixed line or wireless communication interface, or a combination of these. Communication systems providing wireless access typically enable at least some mobility for the users thereof. Examples of these include wireless communications systems where the access is provided by means of an arrangement of cellular access networks. Other examples of wireless access technologies include different wireless local area networks (WLANs) and satellite based communication systems.
A wireless access system typically operates in accordance with a wireless standard and/or with a set of specifications which set out what the various elements of the system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely user equipment, is provided with a circuit switched bearer or a packet switched bearer, or both. Communication protocols and/or parameters which should be used for the connection are also typically defined. For example, the manner in which communication should be implemented between the user equipment and the elements of the networks and their functions and responsibilities are typically defined by a predefined communication protocol.
In the cellular systems a network entity in the form of a base station provides a node for communication with mobile devices in one or more cells or sectors. It is noted that in certain systems a base station is called ‘Node B’. Typically the operation of a base station apparatus and other apparatus of an access system required for the communication is controlled by a particular control entity. The control entity is typically interconnected with other control entities of the particular communication network. Examples of cellular access systems include Universal Terrestrial Radio Access Networks (UTRAN) and GSM (Global System for Mobile) EDGE (Enhanced Data for GSM Evolution) Radio Access Networks (GERAN).
A non-limiting example of another type of access architectures is a concept known as the Evolved Universal Terrestrial Radio Access (E-UTRA). An Evolved Universal Terrestrial Radio Access Network (E-UTRAN) consists of E-UTRAN Node Bs (eNBs) which are configured to provide base station and control functionalities of the radio access network. The eNBs may provide E-UTRA features such as user plane radio link control/medium access control/physical layer protocol (RLC/MAC/PHY) and control plane radio resource control (RRC) protocol terminations towards the mobile devices.
In system providing packet switched connections the access networks are connected to a packet switched core network via appropriate gateways. For example, the eNBs are connected to a packet data core network via an E-UTRAN access gateway (aGW).
Control of the downlink of the E-UTRAN from the base station to the user equipment is carried out based on channel quality indicator (CQI) measured at the user equipment and transmitted to the base station (BS). These calculations are, in general, referred to as link adaptation. Based on this feedback and other factors (these other factors may include system load and delay sensitivity of transmissions) the base station can multiplex different users in time and frequency, and adjust modulation and coding parameters so that time and frequency resources are effectively utilized.
The CQI values are typically generated from Post-detection Signal to Interference and Noise Ratio (SINR) (or where interference is negligible or ignored Signal to Noise Ratio (SNR)) estimates.
In case of a single input multiple output (SIMO) interference rejection combining (IRC) receiver the calculation of post-detection SINR can be shown to be a calculation of symbol amplitude at the output of the antenna combiner unit.
However, these estimates are biased, which can become an issue where absolute values are required. The receiver may have one or several antennas. In the below examples we show two RX antennas. As is known from the IRC receiver the received signal after FFT at a certain subcarrier can be presented as (subcarrier index neglected)
      r    =                  (                                                            r                1                                                                                        r                2                                                    )            =                                                  (                                                                                          h                      1                                                                                                                                  h                      2                                                                                  )                        ⁢            b                    +                      (                                                                                n                    1                                                                                                                    n                    2                                                                        )                          =                  hb          +          n                      ,where h is a channel vector (which is formed from the two channel estimates h1, and h2 from the transmitter to the first and second antenna), b is the unknown data symbol, and n is noise vector.
The IRC receiver has an antenna combiner having coefficients
      w    =                  (                                                            w                1                                                                                        w                2                                                    )            =                        C          nn                      -            1                          ⁢                  h          ^                      ,where Cnn−1 is inverse spatial noise covariance matrix of the subcarrier in question and ĥ is estimate of channel vector h.
IRC antenna combiner output (the combination of the combiner and the received signal) is then given by
                    z        =                                            w              H                        ⁢            r                    =                                                    w                1                *                            ⁢                              r                1                                      +                                          w                2                *                            ⁢                              r                2                                                                            =                                                                                                  w                    H                                    ⁢                  h                                                  ︸                  A                                            ⁢              b                        +                                                            w                  H                                ⁢                n                                            ︸                e                                              =                      Ab            +            e                              
The SINR in this situation is defined as the
                    SINR        =                ⁢                                                          A                                      2                                Var            ⁡                          (              e              )                                                              =                ⁢                                                                                            w                  H                                ⁢                h                                                    2                                E            ⁡                          (                                                                                                            w                      H                                        ⁢                    n                                                                    2                            )                                                              =                ⁢                                                                                            w                  H                                ⁢                h                                                    2                                              w              H                        ⁢                          C              nn                        ⁢            w                                                            =                      w            =                                          C                nn                                  -                  1                                            ⁢              h                                      ⁢                ⁢                                                                                            w                  H                                ⁢                h                                                    2                                              w              H                        ⁢                          C              nn                        ⁢                          C              nn                              -                1                                      ⁢            h                                                  =                ⁢                                                                                            w                  H                                ⁢                h                                                    2                                                                          w                H                            ⁢              h                                                                          =                ⁢                              w            H                    ⁢                      h            .                              These formula and equations however do not account for errors in estimating the values. As such they include these errors which bias the estimation of the signal to noise ratios.